Method and apparatus for depositing particles on a moving web of material

ABSTRACT

An arrangement for depositing particles onto a moving material web includes a particle dispenser and a perforated belt which moves over the material web. According to the invention, the particle dispenser is intended to dispense particles continuously in a uniform and wide flow whose width is equal to or somewhat greater than the width of the hole-pattern of the belt and the belt is spaced at a distance from the material web which is at least sufficiently large for the particles deposited on the material web to be accommodated between the belt and the web. The arrangement also includes means which function to remove particles caught by the belt without the particles falling down onto the underlying material web. These means are located downstream of the particle dispenser. The invention also relates to a method for depositing particles to a moving material web.

This application is a Section 371 continuation of PCT/SE92/00271, filedApr. 24, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and to apparatus fordepositing particles on a moving web of material through theintermediary of a perforated belt which moves over the web.

2. Description of Related Art

The absorbent material used in disposable absorbent products, such asdiapers, sanitary napkins, incontinence guards, wound dressings and thelike, is normally comprised mainly of absorbent fibres, such ascellulose fibres. Absorbent bodies, or pads, which are comprised mainlyof cellulose fibres have certain drawbacks, however. For instance, theability of such bodies to retain the liquid absorbed is poor,particularly when the absorbent body is subjected to load or pressure.Furthermore, the total capacity of such absorbent bodies to absorbliquid is restricted and such bodies quickly become saturated despitethe good liquid-spreading, or liquid-dispersing properties of thefibres.

With the intention of overcoming these drawbacks, there has beendeveloped an absorbent material which has a much greater absorbency thancellulose fibres. These so-called superabsorbents are polymers whoseliquid absorption capacity is many times the intrinsic weight of thepolymers. Although superabsorbents have good liquid retention abilities,they are unable to spread or disperse liquid to the same good extent.Furthermore, superabsorbents swell while absorbing liquid, therebyforming gels which are liable to deny the liquid access to still unusedabsorbent material. This may result in so-called gel blockaging.

Superabsorbents may be comprised of different types of polymers and areproduced in several different forms, for instance in film or particleforms. This latter form is often used for superabsorbents which areintended as absorbent material for use in disposable diapers, forinstance. By "particle form" is meant here all types of material whichexist in powder, flake, granular, short-fibre form and like forms.

Different methods for introducing particulate superabsorbents intoabsorbent bodies have been proposed. "Particulate superabsorbents" willbe referred to in the following as "superabsorbent particles" or simplyas "particles".

WO 87/00057 teaches a method and an arrangement of apparatus of the kindmentioned in the introduction for forming cavities in a moving fibre webwith the aid of a roll provided with a pattern of outwardly-protrudingteeth, wherein the cavities thus formed are filled with superabsorbents.The superabsorbents are delivered to the fibre web intermittently, bymeans of a particle feeder or dispenser mounted above the fibre web, anda scraper which is mounted downstream of the particle feeder and whichfunctions to move those particles which have landed outside the cavitiesdown thereinto. The superabsorbent particles introduced into thecavities are then pressed against the cavity bottom by a second toothedroller having the same tooth pattern as the first roller. The tworollers must therefore be driven exactly synchronously in relation toone another and to the underlying fibre web, in order for the teeth ofthe latter roller to enter the cavities formed by the teeth of the firstroller, and to this end the arrangement includes a drive belt which isprovided with a hole-pattern corresponding to the tooth pattern of therollers and which is intended to pass around said rollers. The drivebelt is also arranged for abutment with the fibre web, so as to ensurethat no superabsorbent particles will land on the upper side thereof.This known arrangement can therefore not be used to deliver a layer ofsuperabsorbent particles to the upper surface of a material web.

Another method is one of mixing the particles with pulp fibres in theair flow which enters the former. This results in a more or lesshomogenous mixture of cellulose fibres and superabsorbent particles.

Another method of introducing superabsorbent particles into absorbentbodies involves layering the particles on a material web. This web maybe moveable and may be comprised, for instance, of cellulose fluff,tissue, non-woven fabric or the like. The layer of superabsorbentmaterial may then be covered with a further web of material, if desired.Different types of binder can be used to bind the particles firmly tothe material web, for instance water or steam. None of the methods knownat present for laying superabsorbent particles onto a moving materialweb will enable sharply defined, discrete particle regions to beobtained when the web is moving at a high speed. This isdisadvantageous, of course, since a high production rate is highlysignificant to production volume.

For instance, it has been proposed to strew superabsorbent particlesonto a passing material web, via a rotating roller. An attempt has beenmade to cover discrete areas or regions of the web with particles, byalternately starting and stopping the roller. An alternative methodinvolves the arrangement of discrete hollows on the peripheral surfaceof the roller from which superabsorbent particles can be strewn onto thepassing web as the roller rotates. None of these methods can be appliedsatisfactorily in practice at high web speeds when desiring the creationof discrete patterns of application in the form of sharply definedparticle regions in absorbent bodies. Neither do these known methodsenable their application patterns to be modified or changed in a simpleand quick fashion.

OBJECTS AND SUMMARY

An object of the present invention is to overcome the aforesaiddrawbacks by means of a method which will enable superabsorbentparticles to be disposed continuously in a specific, well-defined anddiscretely arranged pattern on the Upper surface of a material web whichmoves at a relatively high speed.

An inventive method is mainly characterized by feeding the particlescontinuously from a particle feeder or dispenser in a uniform and wideflow whose width is equal to or slightly greater than the width of thehole-pattern of the web; depositing the particles to the material web indiscrete layers with uniformly distributed particles, the configurationof each layer being determined by the configuration of respective holes;and removing from the belt those particles that are caught thereonwithout said particles falling down onto the underlying material web andwithout disturbing the discrete particle layers applied to said web bysaid removal of said particles.

These advantages afforded by the inventive method are that sharplydefined, discontinuous particle regions of uniform particle distributioncan be obtained in layers of particles produced continuously on a movingmaterial web.

Furthermore, superabsorbent particles can be laid with good precisionand reproduceability on a material web which moves at high speed.

Another advantage is that the configuration of the particle-coveredregions can be changed readily and quickly, by changing the perforatedbelt or masking web for another belt or web.

An inventive arrangement for delivering particles to a moving materialweb comprises a particle dispenser and a perforated belt which movesover the material web. The arrangement is characterized in that theparticle dispenser is constructed to dispense particles continuously ina uniform and wide stream, the width of which is equal to or slightlygreater than the width of the hole-pattern of the belt; in that the beltis spaced from the material web; by a distance which is at leastsufficiently large to accommodate the layer of particles between saidbelt and said web; and in that the arrangement includes means forremoving particles that have been caught by the belt without saidparticles falling down onto the underlying material web, said meansbeing located downstream of the particle feeder.

This arrangement enables the thickness of the layers and thedistribution of particles therein to be varied, by varying the relativespeed and/or the distance between the material web and the belt, therebyrendering the arrangement extremely flexible.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toexemplifying embodiments thereof illustrated in the accompanyingdrawings.

FIG. 1 is a perspective view of one embodiment of an inventivearrangement intended for layering particles on a moving web of material.

FIG. 2 is a schematic side view of the same embodiment as thatillustrated in FIG. 1.

FIG. 3 illustrates a particle dispenser included in the arrangementillustrated in FIGS. 1 and 2.

FIG. 4 is a sectional view taken on the line A--A in FIG. 3.

FIG. 5 is a sectional view taken on the line B--B in FIG. 3.

FIG. 6 is a sectional view taken on the line C--C in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates the transportation of superabsorbent particles 1 froma depot (not shown) through a transport conduit 2, for instance a pipe,to a dispensing device 3, for instance a screw dispenser. The particles1 are then fed from the dispenser 3, via a screw device 4, down onto themasking web or perforated belt 5 moving therebeneath, and down onto afirst material web 6 which travels beneath the masking web 5.

The masking web 5 and the first material web 6 preferably move at thesame speed and in the same direction. The outlet part 7 of the screwdevice 4 roughly defines a right angle with the direction of movement ofthe webs 5, 6. The outlet part 7 is comprised of a slot 8 which extendsin the longitudinal direction of the screw device 4 and which is formedin the outer casing of said screw device. The screw device 4 and itsoutlet part 7 will be described in more detail with reference to FIGS.3-6 below. In order to understand the FIG. 1 illustration, however, itis mentioned now that the particles 1 are dispensed through the slot 8in the outlet part 7 as the screw rotates, and that the width of thethus dispensed flow of particles in relation to the movement directionof the webs 5, 6 is determined by the length of the slot 8.

This width-defined particle-flow is fed down onto a sloping surface 9and the particles 1 falling down from the slot are distributed uniformlyacross the width of said surface prior to falling down onto the maskingweb 5 in the form of a uniform curtain of particles.

The masking web 5 is comprised of an endless belt which moves in a patharound two forward drive rolls 10, 11 in the direction of the arrowsshown. The drive source and associated drive mechanism are not shown inFIG. 1.

The masking web 5 has formed therein a plurality of identical holes 12through which a large number of the particles 1 fall down onto the firstmaterial web 6 moving beneath the masking web 5, said particles 1 beingdeposited in specific, discrete regions 13 whose configuration and sizecoincide with the configuration and size of the holes 12 in the maskingweb 5. A number of particles 14, however, will remain on the masking web5, namely those particles which fall onto the space between the holes 12and those which fall onto side areas of said holes. These particles 14accompany the masking web 5 and are removed therefrom by means of asuction device 15 located upstream of the forward drive roll 11, whichis mounted downstream of the particle dispenser 3. In order to preventremoval by suction of those particles 1 which have been deposited on thefirst material web 6, a screen 16, or some like device, is mountedbetween the webs 5, 6 beneath the suction device 15. The particles 14removed by the suction device are returned to the transport conduit 2,through a further transport conduit 17, and from there to the dispenser3. As will be understood, the transport conduits 17 through which theparticles 14 removed by said suction device are conveyed may leaddirectly to the dispenser 3 or back to the depot. Alternatively, meansfor returning the particles 14 removed by said suction device may bedispensed with and production carried out with solely the removal ofthese particles from the masking web 5.

The masking web 5 turns around the forward drive roll 11 and moves backabove the suction device 15 and the screw device 4 and finally turnsaround the forward drive roll 10, thus completing a full cycle.

The size and the shape of the holes 12 is optional. The holes 12 shownin FIG. 1 are rectangular in shape, although other shapes areconceivable, of course, such as circular, elliptical or triangular holepatterns or combinations thereof. In the FIG. 1 embodiment, the holes 12are arranged sequentially, although it will be understood that two ormore holes may be arranged in the width direction and may also bedisplaced relative to one another in the longitudinal direction of theweb. The masking web 5 is made of particle-impenetrable material, forexample a fabric-reinforced polymer band.

FIG. 2 illustrates schematically the same process as that illustrated inFIG. 1. The transport conduits 2, 17 and the dispenser 3 are not shownin the drawing, however. FIG. 2 illustrates the process stage in whichthe first material web 6 passes beneath the suction device 15, thescreen 16 and the forward drive roll 11 of the masking web 5, subsequentto having deposited particles on the first material web 6. A secondmaterial web 18 is advanced from a reel 19 and is brought into contactwith the first material web 6 such that the particle regions 13 will becovered by the second web 18. The combined webs 6, 18 are moved inbetween two compression rolls 20, 21, thereby locking the particles 1firmly between the two webs 6, 18 by compression.

The compressing process can be completed with other methods which areknown to firmly lock the superabsorbent particles together, for instancemethods which involve the use of binder coatings or spraying of theparticles and/or material webs with water or steam.

Upon exiting from the compression rolls 20, 21, the material webs 6, 18are conveyed to following process stages (not shown), which may involvefolding and cutting of the webs to form individual absorbent bodies. Itis also conceivable to cover the first and the second material webs 6,18 with additional particle-coated material webs prior to said followingprocess stages, in order to create several separate, superimposedparticle regions. These additional material webs may suitably be coatedwith particles in the same manner as the material webs 6, 18 of the FIG.2 embodiment. The material webs may comprise webs of, e.g., cellulosefluff, tissue, non-woven fabric or perforated plastic.

As will be seen from FIGS. 1 and 2, the masking web 5 is spaced from thematerial web 6. In order to obtain sharp and well-defined edges aroundthe applied particle layers 13, the distance between said webs shouldnot exceed 100 mm and will preferably be shorter than 15 mm. Thisdistance must also be sufficient to ensure that the particle layers 13will pass freely from the masking web 5 and freely from the screen 16.It will be understood, however, that the shorter the distance betweenthe web 5 and the material web 6 the greater the risk of diffuse edgesaround the layers 13. In order to ensure that this distance can be madeas short as possible, the material web 6 may be permitted to move in apath which is slightly inclined to the masking web 5, such that the partof the web 5 at which the suction device 15 and the screen 16 are placedwill be located at a greater distance from the material web 6 than isthat part of the web at which the particle dispenser is placed. It ispreferred, however, that the masking web 5 and the material web 6 extendparallel with one another and move at the same speed, so that thosesuperabsorbent particles which may fall down through any of the holes 12from the masking web from that part of the web 5 which moves between theparticle dispenser and the suction device will definitely fall down ontothe material web 6 into one of the particle layers 13 already laid onsaid web. Particles which land outside these layers are liable to damagethe clipping or cutting tools used to cut the material webs 6, 18 intoindividual absorbent products. For the same reason, it is preferred thatthe web 5 will move in the same direction as the material web 6. It isthus important to ensure that no particles will land outside the edgesof the particle layers 13.

It will be understood from the aforegoing that when wishing to utilizethe possibility of varying the extension of the particle layers, byvarying the speed at which the masking web 5 moves in relation to thematerial web 6, the masking web should be configured so that particleswhich land around the edges of the holes 12 in the section of the web 5located between the particle dispenser and the suction device 15 will beretained on said edges, for instance by providing the web 5 with a roughsurface. From the aspect of safety, a web of this configuration is alsosuitable in the earlier described operating conditions.

The illustrated embodiment of the inventive arrangement has been testedwith a spacing between the material web 6 and the masking web 5 of from5-15 mm. When operating the arrangement within this spacing range, ithas been found that the particle layers 13 will have well-defined, sharpedges beth immediately after being deposited and also after havingpassed the suction device 15.

FIG. 3 illustrates dispensing of particles 1 and the laying of saidparticles on the first material web 6 in more detail. For the sake ofillustration, the masking web and the forward drive roll 10 have beenomitted from the Figure.

The particles 1 are dispensed from the dispenser 3 by means of the screwdevice 4 and its screw 4'. A vibratory device may be coupled to thescrew device in order to facilitate dispensing of the particles.

The threads 22 of the screw 4' are shown in broken lines. The outletpart 7 is comprised of a longitudinally extending part of the screwdevice 4, in which a slot 8 has been formed in the outer casing of saiddevice. The slot is of an elongated-arcuate shape and extends from ahighest position 23 at the beginning of the outlet part 7, to a lowestposition 24 at the end of said outlet part. The arcuate shape is adaptedto the transportation properties of the particles, i.e. in accordancewith their ability to run or flow. The slot 8 need not be arcuate,however, but may be linear instead. The inclination of the slot iscontingent on the length of the outlet part. As the screw rotates,particles are transported forwardly towards the outlet part 7,whereafter the particles are dispensed successively through the slot 8.This is shown in detail in FIGS. 4-6.

FIG. 4 illustrates how the particles 1 are advanced in the screw device4 in a stage prior to having reached the outlet part 7 and therewith theslot 8. In the FIG. 5 illustration, the screw 4' has advanced theparticles 1 to a point equal to roughly half the length of the slot,wherein roughly half of the particles having already been dispensed.

FIG. 6 shows the particles located almost at the outermost, andtherewith the lowest position 24 of the slot 8, in which position thelast particles 1 are also fed from the screw 4'.

Thus, a number of particle flows 25 are dispensed from the screw device4 and fall down onto the inclined surface 9. These particle flows aremixed across the width of the inclined surface into a single more orless uniformly distributed particle flow which falls down in the form ofa curtain onto and through the masking web 5 (not shown) and thereafteronto the first material web 6.

The invention shall not be considered limited to the described andillustrated embodiments thereof, since a number of variants areconceivable within the scope of the following Claims.

For example, it is conceivable for the screw device to be angled inrelation to the masking web instead of being straight.

The slot in the particle dispenser may also be divided into alongitudinally extending row of small slots which are mutually separatedby residual parts of the outer casing of the dispenser.

It is also possible, of course, to remove superfluous particles from themasking web in a manner other than by suction. For example, theseparticles may be brushed or scraped away with the aid of appropriatemeans.

Although the invention has been described with reference to the use ofsuperabsorbent particles, it will be understood that the invention canalso be applied with other particulate material which is to be appliedin specific, discrete regions on a material web. An example of suchdifferent material is fragmented thermoplastic material.

I claim:
 1. An arrangement for depositing particles onto a movingmaterial web, said arrangement comprising:a particle dispenser; aperforated belt which moves over the material web; the particledispenser includes means for dispensing the particles continuously in auniform and wide flow whose width is equal to or greater than the widthof a hole-pattern of the belt; the perforated belt extends in a samedirection as the material web; the belt is spaced from the material webat a distance which is at least sufficient to accommodate the particlesdeposited on the material web between said belt and said web; and thearrangement includes means for removing particles which have been caughtby the belt without the particles falling down onto the underlyingmaterial web, said means being located downstream of the particledispenser.
 2. The arrangement of claim 1, further comprising a screwdevice in the particle dispenser for uniformly distributing theparticles over the moving web.
 3. An arrangement according to claim 1,wherein the means for removing particles caught by the belt include asuction device which is mounted immediately above the particle-coatedpart of the belt downstream of and at a distance from the particledispenser, and a screen which is mounted beneath the belt at thelocation of the suction device such as to shield the material web fromthe influence of the suction device.
 4. An arrangement according toclaim 3, wherein the belt moves past the means for removing particlescaught by the belt at a greater distance from the material web than atthe location of the particle dispenser.
 5. An arrangement according toclaim 3, wherein the perforated belt has a rough surface on that sidethereof on which particles are caught.
 6. An arrangement according toclaim 5, wherein the belt moves past the means for removing particlescaught by the belt at a greater distance from the material web than atthe location of the particle dispenser.
 7. An arrangement according toclaim 1, wherein the perforated belt has a rough surface on that sidethereof on which particles are caught.
 8. An arrangement according toclaim 7, further comprising means for varying the relative speed betweenthe perforated belt and the material web.
 9. An arrangement according toclaim 8, wherein the belt moves past the means for removing particlescaught by the belt at a greater distance from the material web than atthe location of the particle dispenser.
 10. An arrangement according toclaim 7, wherein the belt moves past the means for removing particlescaught by the belt at a greater distance from the material web than atthe location of the particle dispenser.
 11. An arrangement according toclaim 1, wherein the belt moves past the means for removing particlescaught by the belt at a greater distance from the material web than atthe location of the particle dispenser.
 12. A method for depositingparticulate material onto a moving web of fibrous material through theintermediary of a perforated masking belt which moves at a distanceabove said web, so as to deposit the particulate material onto the webof fibrous material in discrete layers of uniformly distributedparticles, comprising the steps of:driving the perforated belt in a samedirection as the underlying web of fibrous material; dispensing theparticles continuously from a particle dispenser in a uniform flow whosewidth is equal to or greater than a width of holes in the masking belt,so that the particulate material falls down through the holes in themasking belt and deposits on the web of fibrous material in aconfiguration corresponding to a hole pattern in the masking belt; andremoving from the masking belt those particles which have been caught bysaid belt without falling down onto the underlying web of fibrousmaterial and without said removal having a disturbing influence on thediscrete particle layers deposited on said web of fibrous material. 13.A method according to claim 12, characterized by driving the perforatedbelt at the same speed.
 14. A method according to claim 13, furthercomprising placing a second material web on top of the material web onwhich discrete layers of particles have been deposited and then joiningthe two material webs together by compression.
 15. A method according toclaim 12, characterized by driving the perforated belt and the materialweb at different speeds.
 16. A method according to claim 15, furthercomprising placing a second material web on top of the material web onwhich discrete layers of particles have been deposited and then joiningthe two material webs together by compression.
 17. A method according toclaim 12, further comprising placing a second material web on top of thematerial web on which discrete layers of particles have been depositedand then joining the two material webs together by compression.
 18. Themethod of claim 12, further comprising the step of using a screw deviceto uniformly distribute the particles.
 19. A method of making acomposite material that includes a fibrous material with particulatematerial thereon, comprising the steps of:moving a web of fibrousmaterial in a given direction; driving a masking belt having a pluralityof perforations in a hole pattern therein in the given direction at adistance above said fibrous material; depositing in a uniform flow alayer of particulate material onto the masking belt, said uniform flowhaving a width that equals or exceeds a width of the perforations sothat the particulate material falls down through the perforations in themasking belt and is deposited on the fibrous material in a configurationcorresponding to the hole pattern in the masking belt; and removing fromthe masking belt the particulate material which has been caught by themasking belt without disturbing the particulate material deposited onsaid fibrous material.
 20. The method of claim 19, wherein the web offibrous material and the masking belt move at the same speed.
 21. Themethod of claim 19, wherein the web of fibrous material and the maskingbelt move at different speeds.
 22. The method of claim 19, furthercomprising the step of placing a second fibrous material on top of theweb of fibrous material on which the particulate material has beendeposited and then joining the two fibrous materials together bycompression.
 23. The method of claim 19, further comprising the stepsof:providing a screen between the masking belt and the fibrous materialat a location downstream from a location wherein the particulatematerial is deposited on the fibrous material; and removing theparticulate material from the masking belt with a suction device wherethe masking belt passes over the screen.
 24. The method of claim 19,further comprising the step of using a screw device to evenly distributethe particulate material over the width of the uniform flow.